Need to separate networks at Layer 3
 
 - Multiple IP subnets
- Separate different classes of machines - especially different levels of trust- Access networks: for customers to connect to the Internet (leased lines, modems etc)
- Service networks: machines which we own and manage (mail servers etc)
- Hosted servers: machines which customers own but locate in our facilities
- Office network - should be firewalled anyway
 
- Can also gain some resilience- e.g. put DNS caches on separate networks
 
 Notes: 
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